During the fabrication of multilayer structures such as SeOI (semiconductor-on-insulator) type structures for electronic, microelectronic, and optoelectronic applications, it is routine to interpose insulating layers between wafers of semiconductor materials such as silicon wafers, for example.
Further, it may be necessary to form microcavities or microbubbles in the insulating structure. This applies, in particular, when the structure is to be capable of being taken apart at the insulating layer, as described in International Patent Publication WO 2005/034218A.
The document “Structural and Nuclear Characterizations of Defects Created by Noble Gas Implantation in Silicon Oxide” by H. Assaf et al., Nuclear Instruments and Methods, B 253 (2006), 222-26, for example, describes a method of forming microbubbles in a layer of silicon oxide (SiO2) in order to reduce the value of the dielectric constant k of the oxide layer and, as a result, its permittivity. The method described in that document consists of implanting a layer of SiO2 formed on a silicon substrate with heavy rare gas ions such as xenon. Implantation allows microbubbles to be formed in the SiO2 layer.
However, that method requires the use of heavy rare gas ions, which involves the use of particular ion sources and of more expensive equipment (implanter). Implantation with heavy ions requires higher implantation energy and generates more damage in the implanted material compared with implantation carried out with hydrogen or helium ions, for example. Further, with such ions, it is difficult to control the implantation depth of the ions in the oxide layer and, as a result, the zone over which the microbubbles extend.
There now exists a need to be able to form insulating layers comprising cavities in substrates in a manner that is accurate and economical.